Quantum dot sensitized solar cell based on TiO₂/CdS/CdSe/ZnS heterostructure

A cascade structure of TiO₂/CdS/CdSe/ZnS quantum dot sensitized solar cell (QDSSC) is achieved to boost the photoconversion efficiency of TiO₂/CdSe system by incorporating inner buffer layer of CdS. A sodium dodecyl sulfate (SDS) surfactant mediated TiO₂ nanorods assembly is prepared by a simple hydrothermal technique. The formation of CdS, CdSe and ZnS thin film over TiO₂ nanorods assembly as a photoanode is carried out by successive ionic layer adsorption and reaction (SILAR) and chemical bath deposition (CBD) techniques. Thus synthesized electrode materials are characterized by XRD, XPS, field emission scanning electron microscopy (FE-SEM), TEM, High resolution-TEM (HR-TEM), STEM-EDS mapping, Optical and solar cell performances. The results designate that the thin film of CdS and CdSe have efficiently covered exterior surfaces of TiO₂ nanorods assembly. The interfacial structure of TiO₂/CdS/CdSe is also investigated and the growth interface is verified. A cautious evaluation between CdSe and CdS/CdSe sensitized cells tells that CdS helps to enhance the further growth of CdSe in the cascade electrodes and improves light harvesting. Under AM 1.5G illumination, the photoanodes show an improved power conversion efficiency of 2.56%, in an aqueous polysulfide electrolyte with short-circuit photocurrent density of 4.80 mA cm^-2 which is 18 times higher than that of a bare TiO₂ nanorods assembly.